fix(telemetry): drop deleted RPC OTel dashboard uid from workload validation

The separate xrpld-rpc-perf-otel dashboard was merged into xrpld-rpc-perf,
so the validation harness must no longer expect it to exist.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker/telemetry/workload/expected_metrics.json

@@ -127,7 +127,6 @@
     "description": "All Grafana dashboards that must render data (UIDs as provisioned on disk under docker/telemetry/grafana/dashboards/).",
     "uids": [
       "xrpld-rpc-perf",
-      "xrpld-rpc-perf-otel",
       "xrpld-transactions",
       "xrpld-consensus",
       "xrpld-ledger-ops",